The present invention relates to new isocyanate-based compositions useful as binders for the production of composite materials.
Composite materials (also called compression-molded materials) such as chipboards, composite boards or other molded bodies are produced by hot molding an inorganic or organic raw material such as a mass of wood chips, wood fibers, or other lignocellulose-containing material, with a binder such as an aqueous dispersion of a urea/formaldehyde resin or a phenol/formaldehyde resin. Isocyanates or isocyanate solutions may be used instead of formaldehyde resins as binders for hardboards (See, e.g., German Auslegeschrift 1,271,984; and German Offenlegungschriften 1,492,507; 1,653,177; and 2,109,686). The use of polyisocyanates as binders improves the stability and moisture characteristics of the composite materials and increases their mechanical strength. Polyisocyanates also have far-reaching process engineering advantages when used as binders. These advantages are discussed in German Offenlegungschrift 2,109,688.
The large-scale, industrial production of composite materials bonded with polyisocyanates (particularly lignocellulose-containing materials such as chipboards, fiberboards and plywood) is, however, impeded by the high adhesiveness of the polyisocyanate. This adhesiveness causes the molded composite to adhere strongly to all metal parts (especially pressing plates made of steel or aluminum) after the hot molding and makes mold release difficult.
Previously proposed methods for solving this release problem each have their disadvantages. Some of those disadvantages are greater than others. Release agents developed especially for use with isocyanates frequently have a good release action but they are unreliable in large-scale application, uneconomical and can also cause defective gluing or coating difficulties in the further processing of boards made with the release agent
German Offenlegungschrift 1,653,178 discloses the production of boards or molded bodies by hot molding mixtures of lignocellulose-containing material and polyisocyanates. In the disclosed process, the pressing plates or molds may be treated with polyhydroxylic compounds (e.g.. glycerol, ethylene glycol, polyester polyols or polyether polyols) before compression molding. The fact that a separate operation is necessary for the application of the release agent and that part of the polyisocyanate is consumed by reaction with the release agent makes this process disadvantageous.
Another approach to improving the release behavior of molded bodies is disclosed in German Offenlegungschrift 2,325,926. In this disclosure, release agents which catalyze the formation of isocyanurate in the isocyanate are used. The disadvantage of this process is that the catalyst has a destabilizing effect on the isocyanate which effectively prevents production of an isocyanate binder which will satisfy a specification.